N3′fP5′ Oligodeoxyribonucleotide Phosphoramidates
J . Org. Chem., Vol. 62, No. 21, 1997 7285
2.06 Hz), 2.45 (1 H, ddd, J ) 13.67, 6.09, 4.06 Hz), 2.24 (1 H,
m), 1.94 (3 H, s), 0.95 (9 H, s), 0.15 (6 H, s). HRMS (FAB+):
calcd for [M + Cs]+, 730.2077; observed, 730.2104.
The crude azide (e104.7 mmol) was dissolved in (warm)
ethanol (1600 mL) and reduced via the general method
described above to afford the crude 3′-amine, which was
purified on silica (2-6% MeOH/CH2Cl2 and then 1% Et3N/6%
MeOH/CH2Cl2) to afford a 60% yield (28.2 g, 63.2 mmol) of
pure 5′-O-(tert-butyldimethylsilyl)-N2-isobutyryl-3′-amino-2′,3′-
dideoxyguanosine, 1g, as an off-white foam. Rf (eluant B) )
0.14. 1H NMR (CDCl3/TMS): δ 8.01 (1 H, s), 6.17 (1 H, dd, J
) 6.77, 3.98 Hz), 3.80-3.90 (4 H, mm), 2.83 (1 H, septet, J )
6.80 Hz), 2.59 (1 H, ddd, J ) 13.26, 6.16, 4.03 Hz), 2.33 (1 H,
dt, J ) 13.19, 6.79 Hz), 1.26 (6 H, dd, J ) 6.86, 2.79 Hz), 0.88
(9 H, s), 0.07 (3 H, s), 0.06 (3 H, s). HRMS (FAB+): calcd for
[M + H]+, 451.2489; observed, 451.2480.
N4-Ben zoyl-5-m eth yl-3′-(tr ityl)a m in o-5′-O-(ter t-bu tyl-
d im eth ylsilyl)-2′,3′-d id eoxycytid in e (2m c). This compound
was synthesized in 81% yield by an analogous method to 2c,
except 2t was employed as the starting material rather than
2d u . N4-Benzoyl-5-methyl-3′-(trityl)amino-5′-O-(tert-butyl-
dimethylsilyl)-2′,3′-dideoxycytidine, 2m c, Rf (eluant C) ) 0.84.
1H NMR (CDCl3/TMS): δ 13.25 (1 H, br s, exchanges in D2O),
8.32 (2 H, d, J ) 7.21 Hz), 7.53 (6 H, d, J ) 7.56 Hz), 7.45 (2
H, t, J ) 7.51 Hz), 7.27-7.42 (8 H, m), 7.23 (3 H, t, J ) 7.23
Hz), 6.27 (1 H, dd, J ) 8.00, 6.05 Hz), 3.89 (1 H, m), 3.75 (1 H,
dd, J ) 11.34, 1.73 Hz), 3.43 (1 H, dd, J ) 11.37, 2.47 Hz),
3.32 (1 H, m), 2.06 (3 H, s), 1.50-1.70 (3 H, m), 0.84 (9 H, s),
0.01 (3 H, s), -0.04 (3 H, s). HRMS (FAB+): calcd for [M +
Cs]+, 833.2499; observed, 833.2476.
5′-O-(ter t-Bu t yld im et h ylsilyl)-N2-isob u t yr yl-3′-(t r it -
yl)a m in o-2′,3′-d id eoxygu a n osin e (2g). The following
amounts were used in the tritylation reaction: Solvent,
pyridine (500 mL), 5′-O-(tert-butyldimethylsilyl)-N
2-isobutyryl-
N4-Ben zoyl-5-m eth yl-3′-(tr ityl)a m in o-2′,3′-d id eoxycyti-
d in e (3m c). This compound was obtained in 95% yield via
desilylation of 2mc as shown in Scheme 3 (and as described in
the syntheses of 3c, 3a , and 3g). N4-Benzoyl-5-methyl-3′-
(trityl)amino-2′,3′-dideoxycytidine, 3mc, Rf (1:1 EtOAc/hexane)
) 0.50. 1H NMR (CDCl3/TMS): δ 13.2 (1 H, br s, exchanges
with D2O), 8.25 (2 H, d, J ) 8.28 Hz), 7.58 (6 H, d, J ) 8.08
Hz), 7.47 (1 H, s), 7.43 (2 H, d, J ) 7.51 Hz), 7.30 (6 H, t, J )
7.50 Hz), 7.22 (3 H, t, J ) 7.21 Hz), 6.03 (1 H, dd, J ) 6.72,
5.36 Hz), 3.90 (1 H, ddd, J ) 11.97, 5.42, 2.16 Hz), 3.76 (1 H,
m), 3.70 (1 H, ddd, J ) 11.98, 5.56, 3.36 Hz), 3.34 (1 H, m),
2.04 (3 H, s), 1.82 (1 H, br d, J ) 8.47 Hz, exchanges with
D2O), 1.55-1.65 (1 H, m), 1.32-1.42 (1 H, m). HRMS
(FAB+): calcd for [M + Cs]+, 719.1634; observed, 719.1653.
Anal. Calcd for C36H34N4O4: C, 73.70; H, 5.84; N, 9.55.
Observed: C, 73.66; H, 6.09; N, 9.15.
3′-amino-2′,3′-dideoxyguanosine, 1g (28.5 g, 63.2 mmol), tri-
ethylamine (17.6 mL, 126.4 mmol), and trityl chloride (28.2 g,
101.1 mmol). After stirring 16 h at RT, solvents were removed
in vacuo and the residue was purified on silica (1-5% MeOH/
CH2Cl2) to afford a quantitative yield (43.8 g, 63.2 mmol) of
5′-O-(tert-butyldimethylsilyl)-N2-isobutyryl-3′-(trityl)amino-
2′,3′-dideoxyguanosine, 2g. Rf (eluant B) ) 0.72. 1H NMR
(CDCl3/TMS): δ 11.90 (1 H, br s, exchanges with D2O), 8.01
(1 H, br s, exchanges with D2O), 7.58 (1 H, s), 7.56 (6 H, d, J
) 7.39 Hz), 7.31 (6 H, t, J ) 7.58 Hz), 7.23 (3 H, t, J ) 7.28
Hz), 6.00 (1 H, dd, J ) 6.86, 4.63 Hz), 3.88 (1 H, dt, J ) 5.91,
3.01 Hz), 3.75 (2 H, ABX, J AB ) 11.25 Hz), 3.52 (1 H, m), 2.57
(1 H, septet, J ) 6.91 Hz), 2.00- 2.10 (1 H, br s, exchanges
with D2O), 1.72 (1 H, dt, J ) 13.63, 6.89 Hz), 1.59 (1 H, ddd,
J ) 13.73, 6.69, 4.87 Hz), 1.28 (6 H, dd, J ) 6.90, 3.22 Hz),
0.81 (9 H, s), -0.03 (3 H, s), -0.04 (3 H, s). HRMS (FAB+):
calcd for [M + Cs]+, 825.2561; observed, 825.2540. Anal.
Calcd for C39H48N6SiO4: C, 67.60; H, 6.98; N, 12.13. Ob-
served: C, 67.89; H, 7.12; N, 12.01.
5′-O-(ter t-Bu tyld im eth ylsilyl)-N2-isobu tyr yl-3′-a m in o-
2′,3′-d id eoxygu a n osin e (1g). To a stirring solution of 3′-O-
x
benzoyl-N2-isobutyryl-2′-deoxyxyloguanosine, g (4.86 g, 11.0
mmol), in DMF (20 mL), was added triethylamine (3.4 mL,
24.2 mmol), 4-dimethylaminopyridine (54 mg, 0.44 mmol), and
tert-butyldimethylsilyl chloride (3.31 g, 22.0 mmol). The reac-
tion was stirred for 2 h at RT, methanol (10 mL) was added,
and after stirring an additional 5 min, the reaction mixture
was concentrated in vacuo. The residue was redissolved in
CH2Cl2 (150 mL) and washed with H2O (3 × 40 mL) and
saturated aqueous NaCl (60 mL). The organic layer was dried
over Na2SO4, filtered, and concentrated in vacuo to afford 6.40
g (>100% crude yield) of a reddish-colored foam. To this crude
material was added a prechilled (ca. 5 °C) solution of 2 M
aqueous NaOH in either 1:1 MeOH:1,4-dioxane or 65:30:5
pyridine:MeOH:H2O (44.0 mL, 87.9 mmol) at 5 °C. The
reaction mixture was stirred in an ice bath for 15-20 min and
neutralized with 1 M aqueous HCl (97 mL) to pH 6-7. After
the ice bath was removed, the reaction mixture was concen-
trated in vacuo to ca. 50 mL and extracted with CH2Cl2 (3 ×
75 mL). The combined organics were washed with saturated
aqueous NaHCO3 (3 × 50 mL)] and saturated aqueous NaCl
(2 × 50 mL), dried over Na2SO4, filtered, and concentrated in
vacuo to afford an 82% yield (4.1 g, 9.1 mmol) of 5′-O-(tert-
butyldimethylsilyl)-N2-isobutyryl-2′-deoxyxyloguanosine as a
sandy-colored foam, which was taken on to the next reaction
without further purification.
N 2
-Isob u t yr yl-3′-(t r it yl)a m in o-2′,3′-d id e oxygu a n o-
sin e (3g). The following amounts were utilized in the de-
silylation reaction: Solvent, THF (123.0 mL), 5′-O-(tert-but-
yldimethylsilyl)-N2-isobutyryl-3′-(trityl)amino-2′,3′-dideoxygua-
nosine, 2g (42.6 g, 61.5 mmol), and TBAF (1 M in THF, 123.0
mL). The reaction mixture was stirred for 24 h, extracted as
described above in the general desilylation procedure (albeit
substituting EtOAc for CH2Cl2), and purified on silica (packed
in 2% Et3
N in 2% MeOH/CH2Cl2 and eluted with 2-5% MeOH/
CH2Cl2) to afford a 93% yield (33.1 g, 57.2 mmol) of N6-benzoyl-
3′-(trityl)amino-2′,3′-dideoxyguanosine, 3g. Rf
(eluant A) )
0.29. 1H NMR (CDCl3/TMS): δ 11.91 (1 H, br s, exchanges
with D2O), 7.89 (1 H, br s, exchanges with D2O), 7.58 (1 H, s),
7.54 (6 H, d, J ) 7.39 Hz), 7.29 (6 H, t, J ) 7.60 Hz), 7.21 (3
H, t, J ) 7.27 Hz), 5.98 (1 H, t, J ) 6.67 Hz), 4.19 (1 H, dd, J
) 9.26, 1.76 Hz, exchanges with D2
O), 3.86 (1 H, m), 3.82 (1
H, d, J ) 12.26 Hz), 3.70 (1 H, m), 3.50 (1 H, ddd, J ) 10.72,
9.92, 2.00 Hz), 2.55 (1 H, septet, J ) 6.88 Hz), 1.95-2.03 (1
H, br s, exchanges with D2O),1.91 (1 H, dt, J ) 13.58, 6.93
Hz), 1.60 (1 H, ddd, J ) 13.59, 6.48, 4.69 Hz), 1.24 (6 H, t, J
) 6.83 Hz). HRMS (FAB+): calcd for [M + Na]+, 601.2539;
observed, 601.2527. Anal. Calcd for C33
H34N6O4: C, 68.50;
H, 5.92; N, 14.52. Observed: C, 68.23; H, 6.28; N, 14.14.
5′-O-(t er t -Bu t yld im e t h ylsilyl)-N 2-isob u t yr yl-O6-(d i-
p h e n ylca r b a m oyl)-3′-(t r it yl)a m in o-2′,3′-d id e oxygu a -
n osin e (2gd p c). To 5′-O-(tert-butyldimethylsilyl)-N2-isobu-
tyryl-3′-(trityl)amino-2′,3′-dideoxyguanosine, 2g (30.3 g, 43.7
mmol), was added anhydrous pyridine (90 mL), N,N-diisoprop-
ylethylamine (11.4 mL, 65.6 mmol), and diphenylcarbamyl
chloride (11.1 g, 48.1 mmol) under argon. After stirring for
1.5 h at RT, the intensely red/purple reaction mixture was
concentrated in vacuo. The residue was redissolved in CH2Cl2
(600 mL), extracted with H2O (2 × 400 mL) and saturated
aqueous NaCl (400 mL), dried over Na2SO4, filtered, and
concentrated in vacuo. The residue was then redissolved in
CH2Cl2 and azeotroped with toluene (3×). This afforded a
>100% yield (43.8 g) of impure 5′-O-(tert-butyldimethylsilyl)-
N2-isobutyryl-O6-diphenylcarbamoyl-3′-(trityl)amino-2′,3′-
dideoxyguanosine, 2gdpc, which was generally taken on directly
to desilylation (although it could also be purified on silica). Rf
To crude 5′-O-(tert-butyldimethylsilyl)-N2-isobutyryl-2′-
deoxyxyloguanosine (47.3 g, 104.7 mmol) was added LiN3 (15.4
g, 314.1 mmol), triphenylphosphine (41.2 g, 157.1 mmol), and
anhydrous DMF (1000 mL). Diethylazodicarboxylate (24.7
mL, 157.1 mmol) was added and the reaction mixture was
stirred for 5 h at RT under argon. H2O (20 mL) was added
and the reaction mixture was concentrated in vacuo. The
residue was dissolved in EtOAc (1500 mL), washed with H2O
(3 × 1000 mL) and saturated aqueous NaCl (1000 mL), dried
over Na2SO4, filtered, and concentrated in vacuo. The residue
was purified on silica (1-5% MeOH/CH2Cl2), although this
afforded a >100% yield (112.7 g) of impure 5′-O-(tert-butyldi-
methylsilyl)-N2-isobutyryl-3′-azido-2′,3′-dideoxyguanosine. This
crude (triphenylphosphine oxide-contaminated) product was
not purified further and was taken on directly to hydrogena-
tion (and purified as the 3′-amine).